A well known need exists within industries involved with macromolecules to characterize molecules created by or used in various processes. Application areas where this need is of particular interest include quality control laboratories, research laboratories and manufacturing operations in the plastics, pharmaceutical, biotech and chemicals industries. Typical measurements to characterize molecules include determination of the molecular weight distributions and polydispersity when different molecular weights are included in the sample, molecular sizes (hydrodynamic radii, radii of gyration), concentrations and conformation information, including shape information and molecular branching information.
The most common technique for molecular characterization is liquid chromatography (LC), which involves the preparation of the sample for the particular detection method to be used and the detection method itself. In this well known analytical technique, a flowing mixture of a solvent and the substances to be tested (a mixture of molecules with various molecular weights and other molecular characteristics) is passed through specifically selected chromatography columns which result in the component molecules being separated in time in the flowing solvent according to their size or according to some other molecular characteristic. The flowing fluid then passes through the detector. In one type of detector, a laser beam is directed through the fluid, and the scattered light is analyzed to provide molecular characterization.
Examples of uses of liquid chromatography are the analyses of proteins, commercial resins, natural and synthetic polymers, neucleic acids, plasticizers, plant and animal metabolites, lubricants, dyes, petroleum residues, pharmaceuticals, amino acids, pigments, polysaccharides, pesticides, herbicides, fungicides, surfactants, lipids, explosives, and other materials.
The detectors have used various techniques for detecting light scattered by sample molecules. In one prior art system, the sample is surrounded by an array of detectors which collect laser light scattered by the sample at different angles. In another prior art system, laser light scattered by the sample at a predetermined angle passes through an annular aperture and is focused on a photomultiplier. All of the known prior art molecular characterization detectors have had one or more disadvantages, including difficulty of use because of required optical alignment, low signal levels and interference from stray light, which reduces accuracy, and relatively high cost.
It is a general object of the present invention to provide improved methods and apparatus for molecular characterization.
It is another object of the present invention to provide a molecular characterization detector wherein interference from stray light is reduced in comparison with prior art detectors.
It is a further object of the present invention to provide improved molecular characterization instruments.
It is still another object of the present invention to provide a molecular characterization detector wherein light scattered by window surfaces is blocked from reaching the light detector.
It is yet another object of the present invention to provide a molecular characterization detector which is low in cost, easy to manufacture and which does not require optical alignment.